I'm a one, you're a two and you're a three," I shared with two girlfriends as I doused every patch of my skin with SPF 70 sunscreen spray. The numbers refer to the Fitzpatrick skin scale, developed by Harvard dermatologist Thomas B. Fitzpatrick. The scale classifies how different people respond to ultraviolet light – specifically to one hour of sunlight on the first day of spring. So when my friends and I were in Las Vegas this weekend, the intense winter white I cultivated under scrubs and artificial lights all season was ready to burn....